Cooling System for High Power Vacuum Tubes

ABSTRACT

According to one embodiment, a two-phase cooling system includes a condensing heat exchanger fluidly coupled to an evaporator assembly and a pressure controller. The condensing heat exchanger condenses a coolant from a vapor phase to a liquid phase by removing heat from the coolant. The evaporator assembly is thermally coupled to a vacuum tube and operable to receive liquid coolant from the condensing heat exchanger, cool the vacuum tube by evaporating the coolant from the liquid phase to the vapor phase, and transporting the evaporated coolant to the condensing heat exchanger. The pressure controller maintains the pressure of the coolant in the evaporator assembly at a sub-ambient pressure to lower the boiling point of the coolant for reducing the operating temperature of the vacuum tube.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application Ser. No. 60/972,960, entitled “COOLING SYSTEM FOR HIGH POWER VACUUM TUBES,” which was filed on Sep. 17, 2007.

TECHNICAL FIELD OF THE DISCLOSURE

This disclosure generally relates to the field of cooling systems, and more particularly, to a system for cooling vacuum tubes using a coolant that operates at a sub-ambient pressure to lower the boiling point of the coolant.

BACKGROUND OF THE DISCLOSURE

A variety of different types of structures can generate heat or thermal energy in operation. To prevent such structures from over heating and to provide stable operating conditions, a variety of different types of cooling systems may be utilized to dissipate the thermal energy, including two-phase systems in which their constituent coolants change phase from a liquid state to a vapor state or a solid state to a liquid state.

SUMMARY OF THE DISCLOSURE

According to one embodiment, a two-phase cooling system includes a condensing heat exchanger fluidly coupled to an evaporator assembly and a pressure controller. The condensing heat exchanger condenses a coolant from a vapor phase to a liquid phase by removing heat from the coolant. The evaporator assembly is thermally coupled to a vacuum tube and operable to receive liquid coolant from the condensing heat exchanger, cool the vacuum tube by evaporating the coolant from the liquid phase to the vapor phase, and transporting the evaporated coolant to the condensing heat exchanger. The pressure controller maintains the pressure of the coolant in the evaporator assembly at a sub-ambient pressure to lower the boiling point of the coolant for reducing the operating temperature of the vacuum tube.

Certain embodiments of the disclosure may provide numerous technical advantages. For example, a technical advantage of one embodiment may include an enhanced cooling of high-power, vapor cooled vacuum tubes (such as those configured to power radio frequency heating equipment and for high power transmission of radio frequency signals) by lowering the vacuum tube's operating temperatures. A technical advantage of another embodiment may include use of a pressure controller that maintains a suitable coolant (such as water) at a sub-ambient pressure, allowing a reduction of the coolant's effective boiling point. This reduced effective boiling point, in turn, may allow the operating temperature of high-power, vapor cooled vacuum tubes to be reduced for enhanced performance in some embodiments.

Although specific advantages have been enumerated above, various embodiments may include all, some, or none of the enumerated advantages. Additionally, other technical advantages may become readily apparent to one of ordinary skill in the art after review of the following figures and description.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of embodiments of the disclosure will be apparent from the detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of an embodiment of a cooling system that may be utilized in conjunction with other embodiments disclosed herein;

FIG. 2 is a block diagram of another embodiment of a cooling system that may be utilized in conjunction with other embodiments disclosed herein;

FIG. 3 shows one embodiment of a cooling system, according to an embodiment of the present disclosure;

FIG. 4 shows another embodiment of a cooling system for a vapor cooled vacuum tube, according to an embodiment of the disclosure; and

FIG. 5 is a flowchart showing one embodiment of a series of actions that may be performed by the embodiments of FIGS. 1 through 4 to cool a vacuum tube according to the teachings of the present disclosure.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE DISCLOSURE

It should be understood at the outset that although example embodiments of the present disclosure are illustrated below, the present disclosure may be implemented using any quantity of techniques, whether currently known or in existence. The present disclosure should in no way be limited to the example embodiments, drawings, and techniques illustrated below, including the embodiments and implementation illustrated and described herein. Additionally, the drawings are not necessarily drawn to scale.

High power vacuum tubes may be used for various purposes, such as radio frequency (RF) commercial broadcast, exciters for nuclear research, and high power short wave communications. Known cooling systems for these high power vacuum tubes have typically incorporated water as a coolant where some configurations of these high power vacuum tubes are cooled using water that changes phase from a liquid state to a vapor state as heat energy is absorbed. At normal ambient pressure, the resulting vacuum tube component temperatures are generally limited by the temperature of the water phase change that occurs at 100 degrees Celsius. For these types of vacuum tubes to operate at lower temperatures, the boiling point of the water should be lowered. Lowering the boiling point of the water used to cool vapor cooled vacuum tubes, however, has not been possible using known cooling systems.

FIG. 1 is a block diagram of one embodiment of a cooling system 10 that may be utilized in conjunction with other embodiments disclosed herein, namely the embodiments described with reference to FIGS. 3 and 4. Although the details of one cooling system will be described below, it should be expressly understood that other cooling systems may be used in conjunction with embodiments of the disclosure, including the cooling system 100, described with reference to FIG. 2.

Cooling system 10 of FIG. 1 is shown cooling a structure 12 that is exposed to or generates thermal energy. The structure 12 may be any suitable structure for which dissipation of heat is needed or desired. In one embodiment, structure 12 is a vacuum tube. Because a structure 12 such as a vacuum tube can vary greatly, the details of structure 12 are not illustrated and described. Cooling system 10 includes a vapor line 14, a liquid line 16, one or more evaporator assemblies 18 a and 18 b, a pump 20, one or more inlet orifices 22 a and 22 b, a condenser heat exchanger 24, an expansion reservoir 26, and a pressure controller 28.

Structure 12 may be arranged and designed to conduct heat or thermal energy to evaporator assemblies 18 a and 18 b. To receive this thermal energy or heat, evaporator assemblies 18 a and 18 b may be disposed on an edge of structure 12 (e.g., as a thermosyphon, heat pipe, or other device) or may extend through portions of structure 12, for example, through a thermal plane of structure 12. In particular embodiments, evaporator assemblies 18 a and 18 b may extend up to the components of structure 12, directly receiving thermal energy from the components. Although two evaporator assemblies 18 a and 18 b are shown in cooling system 10, one evaporator assembly or more than two evaporator assemblies may be used to cool structure 12 in other cooling systems.

In operation, a fluid coolant flows through each of the evaporator assemblies 18 a and 18 b. As described later, this fluid coolant may be a two-phase fluid coolant, which enters inlet conduits 32 of evaporator assemblies 18 a and 18 b in liquid form. Absorption of heat from structure 12 causes part or all of the liquid coolant to boil and vaporize such that some or all of the fluid coolant leaves the exit conduits 34 of evaporator assemblies 18 a and 18 b in a vapor phase. To facilitate such absorption or transfer of thermal energy, evaporator assemblies 18 a and 18 b may be lined with pin fins or other similar devices which, among other things, increase surface contact between the fluid coolant and walls of evaporator assemblies 18 a and 18 b. In particular embodiments, the fluid coolant may be forced or sprayed into the evaporator assemblies 18 a and 18 b to ensure fluid contact between the fluid coolant and the walls of evaporator assemblies 18 a and 18 b.

The fluid coolant departs exit conduits 34 and flows through vapor line 14, condenser heat exchanger 24, expansion reservoir 26, pump 20, liquid line 16, and a respective one of two inlet orifices 22 a and 22 b, in order to again reach the inlet conduits 32 of evaporator assemblies 18 a and 18 b. Pump 20 transports fluid through evaporator assemblies 18 a and 18 b. In particular embodiments, pump 20 may use magnetic drives such that no shaft seals are implemented, which can wear or leak with time. Although vapor line 14 uses the term “vapor,” it may contain some liquid.

Inlet orifices 22 a and 22 b in particular embodiments may facilitate proper partitioning of the fluid coolant among the evaporator assemblies 18 a and 18 b, and may also help to create a desired pressure drop between the output of pump 20 and evaporator assemblies 18 a and 18 b. Inlet orifices 22 a and 22 b may have the same size, or may have different sizes in order to partition the coolant in a proportional manner to facilitate the removal of different levels of heat from different evaporator assemblies 18 a and 18 b.

A flow 38 of fluid (either a gas such as air or liquid) may be forced to flow through condenser heat exchanger 24, for example by a fan (not shown) or other suitable device. In particular embodiments, the flow 38 of fluid may be ambient air that cools the coolant in condenser heat exchanger 24 using convection currents. The condenser heat exchanger 24 transfers heat from the coolant that may be in the vapor state to the flow 38 of ambient fluid, thereby causing any portion of the fluid coolant which is in the vapor phase to condense back into a liquid phase. In particular embodiments, a liquid bypass 40 may be provided for liquid fluid coolant that either may have exited the evaporator assemblies 18 a and 18 b or that may have condensed from vapor fluid coolant during travel to the condenser heat exchanger 24. In particular embodiments, the condenser heat exchanger 24 may be a cooling tower.

The liquid fluid coolant exiting the condenser heat exchanger 24 may be fluidly coupled to expansion reservoir 26. Since fluids typically take up more volume in their vapor phase than in their liquid phase, the expansion reservoir 26 may be provided in order to take up the volume of liquid fluid coolant that is displaced when some or all of the coolant in the system changes from its liquid phase to its vapor phase. The amount of the fluid coolant which is in its vapor phase can vary over time, due in part to the fact that the amount of heat or thermal energy produced by structure 12 may vary over time, as structure 12 system operates in various operational modes.

Turning now in more detail to the fluid coolant, one relatively efficient technique for removing heat from a surface is to boil and vaporize a liquid which is in contact with a surface. As the liquid vaporizes in this process, it inherently absorbs heat to effectuate such vaporization. The amount of heat that can be absorbed per unit mass of a liquid is commonly known as the latent heat of vaporization of the liquid. The higher the latent heat of vaporization, the larger the amount of heat that can be absorbed per unit mass of liquid that is vaporized.

The fluid coolant used in the embodiment of FIG. 1 may include, but is not limited to, mixtures of antifreeze and water or water, alone. In particular embodiments, the antifreeze may be ethylene glycol, propylene glycol, methanol, or other suitable antifreeze formulations. In other embodiments, the liquid may be a perfluorocarbon, such as octafluoropropane, perfluorohexane, or perfluorodecalin. These perfluorocarbons are relatively inert and generally electrically insulative making them well suited for use around vacuum tubes.

At a typical ambient pressure of 14.7 pounds-per-square-inch-absolute, water boils at a temperature of 100° C. In particular embodiments, the fluid coolant's boiling temperature may be reduced to between 55 to 65° C. by subjecting the fluid coolant to a sub-ambient pressure in the range of approximately 2 to 3 pounds-per-square-inch-absolute. Thus, inlet orifices 22 a and 22 b may permit the pressure of the fluid coolant downstream from them to be substantially less than the fluid coolant pressure between the pump 20 and inlet orifices 22 a and 22 b, which in this embodiment is shown as approximately 12 pounds-per-square-inch-absolute. Pressure controller 28 maintains the coolant at a pressure of approximately 2 to 3 pounds-per-square-inch-absolute along the portion of the loop which extends from the outlet of inlet orifices 22 a and 22 b to the inlet of pump 20, in particular through evaporator assemblies 23 and 24, condenser heat exchanger 24, and expansion reservoir 26. In particular embodiments, a metal bellows may be used in the expansion reservoir 26 and coupled to the loop using any suitable approach, such as with brazed joints. In particular embodiments, pressure controller 28 may control loop pressure using a motor driven linear actuator coupled to the metal bellows or by using a small gear pump that evacuates the loop to the desired pressure level. The fluid coolant removed may be stored in the metal bellows. In other configurations, pressure controller 28 may utilize other suitable devices capable of controlling pressure.

In particular embodiments, the fluid coolant flowing from pump 20 to inlet orifices 22 a and 22 b through liquid line 16 may have a temperature of approximately 55° C. to 60° C. and a pressure of approximately 12 pounds-per-square-inch-absolute as referenced above. After passing through inlet orifices 22 a and 22 b, the fluid coolant may still have a temperature of approximately 55° C. to 60° C., but may also have a lower pressure in the range of approximately 2 to 3 pounds-per-square-inch-absolute. Due to this reduced pressure, fluid coolant in the liquid state can absorb heat by boiling within evaporator assemblies 18 a and 18 b where the boiling occurs at a temperature less than 100 degrees Celsius.

After leaving exit conduits 34 of evaporator assemblies 18 a and 18 b, the sub-ambient coolant vapor travels through vapor line 14 to condenser heat exchanger 24 where heat or thermal energy can be transferred from the coolant vapor to the flow 38 of fluid. The flow 38 of fluid in particular embodiments may have any temperature less than the temperature of the fluid coolant, such as 50° C. or 40° C. As heat is removed from the fluid coolant, any portion of the fluid coolant that is in its vapor phase will condense such that all or most of the coolant will be in liquid form when it exits condenser heat exchanger 24. At this point, the fluid coolant may have a temperature of approximately 55° C. to 60° C. and a sub-ambient pressure of approximately 2 to 3 pounds-per-square-inch-absolute. The liquid coolant may then flow to pump 20, which in particular embodiments may increase the pressure of the fluid coolant to a value in the range of approximately 12 pounds-per-square-inch-absolute. There may be a fluid connection to an expansion reservoir 26 which, when used in conjunction with the pressure controller 28, controls the pressure within the cooling loop.

It will be noted that the embodiment of FIG. 1 operates without a refrigeration system. In the context of electronic circuitry, such as may be utilized in the structure 12, the absence of a refrigeration system can result in a significant reduction in the size, weight, and power consumption of the structure provided to cool the circuit components of structure 12.

FIG. 2 is a block diagram of another embodiment of a cooling system 100 that may be utilized in conjunction with other embodiments disclosed herein, namely the embodiments described with reference to FIGS. 3 and 4. Cooling system 100 may operates generally similar to cooling system 10 of FIG. 1; however, cooling system 100 of FIG. 2 also incorporates an air removal system 190. For a variety of reasons, unintended air may be introduced into cooling system 100. For example, in embodiments operating at sub-ambient pressure, outside ambient air may leak into the sub-ambient system due to a leak in the system. Accordingly, cooling system 100 may utilize air removal system 190 to remove this unwanted air from cooling system 100. Air removal system 190 in the embodiment of FIG. 2 includes an air pump 192, a reclamation heat exchanger 194, coolant reservoir 196, and a reclamation fill valve 198.

With reference to FIG. 2, the cooling loop of cooling system 100 including an evaporator 118, a pump 120, a liquid line 116, a vapor line 114, an expansion reservoir 126, a pressure controller 128, and a condenser heat exchanger 124 is similar to the cooling loop for cooling system 10 of FIG. 1. Fluid or air leaks 102 may enter the cooling loop at evaporator assembly 118 or other location and travel in vapor line 114 to the condenser heat exchanger 124. At condenser heat exchanger 124, vaporized coolant will condense to a liquid while the leaked air that cannot condense will accumulate in areas of condenser heat exchanger 124 where the velocity of the air is greatly reduced. Accumulated leakage air and any associated vapor coolant that may be present in the form of humidity may be pumped using air pump 192 to reclamation heat exchanger 194. Reclamation heat exchanger 194 cools the air/vapor coolant combination, which condenses the vapor from the air stream being removed from the bottom of the condenser heat exchanger 124. Condensed coolant separates from the air in coolant reservoir 196 while the air exits through vent 195. A level switch 197 may be in communication with a reclamation fill valve 198 to allow the reclamation fill valve 198 to open when recovered coolant is present. The recovered coolant may be reintroduced to the cooling loop through reclamation fill valve 198 and a conduit in communication with pump 120.

Although one example of an air removal system 190 has been shown with reference to FIG. 2, other air removal systems may be used in other embodiments of the disclosure with more, less, or alternative component parts. Additionally, although components of embodiments of cooling system 10 and 100 have been shown in FIGS. 1 and 2, it should be understood that other embodiments of the cooling system 10 can include more, fewer, or different component parts. For example, although specific temperatures and pressures have been described for such one embodiment of cooling systems 10 and 100, other embodiments of cooling system 10 and 100 may operate at different pressures and temperatures.

FIG. 3 shows one embodiment of a cooling system 200 that is retrofitted from a known cooling system that is used to cool a vacuum tube 202. Cooling system 200 of the present disclosure differs from known cooling system in that cooling system 200 may be operable to cool vacuum tubes 202 at temperatures below 100 degrees Celsius. For example, cooling system 200 of FIG. 3 incorporates a fluid coolant that operates at a sub-ambient pressure in the range of 1 to 3 pounds-per-square-inch-absolute such that the boiling point of its water coolant cools vacuum tube 202 to between 40 to 60 degrees Celsius.

Although the system 200 of FIG. 3 is retrofitted from a known cooling system, it should be understood that other embodiments may retrofit other known cooling systems to provide sub-ambient cooling. In other embodiments, some, none, or all of the components of known cooling systems may be utilized. With this embodiment and other embodiments described herein, any of a variety of methods that keep water as an insulator may be utilized. Such methods are common practice with vapor and water cooled vacuum tubes.

In the embodiment of FIG. 3, cooling system 200 has components similar to the cooling systems 10 and 100 of FIGS. 1 and 2. For example, cooling system 200 has a vapor line 214, a liquid line 216, an evaporating heat exchanger 218, a condensing heat exchanger 224, an expansion reservoir 226, a pressure controller 228, and a liquid bypass and an equalization line 240. Each of these components may operate in a similar or different manner than the respective components described with reference to FIGS. 1 and 2. Evaporating heat exchanger 218 of this type is generally referred to as a “pool boiling mechanism.”

Cooling system 200 also includes a control box 242, a solenoid valve 244, and a make-up reservoir 246 that form a portion of the known cooling system. Control box 242 may be provided to control various aspects of cooling system 200 including operating pressures and/or flow rate of fluid coolant. Solenoid valve 244 operates with make-up reservoir 246 to store additional fluid coolant and provides this additional fluid coolant to cooling system 200 on an as needed basis. In other embodiments, more less or different components of a known cooling system may be used for retrofitting cooling system 200.

In this disclosure, the term “subambient pressure” generally refers to a pressure of fluid coolant that is less than normal ambient pressure of approximately 14.7 pounds-per-square-inch. In particular embodiments, cooling system 200 may provide an advantage over known cooling systems in that the sub-ambient pressure of the fluid coolant may cool vacuum tube 202 at a relatively lower temperature than provided by known cooling systems. In a particular embodiment in which the coolant is water, cooling system 200 may enable vaporization of water receiving thermal energy from vacuum tube 202 at temperatures below 100 degrees Celsius that my result in lower vacuum tube anode and seal temperatures than if the water has boiled at 100 degrees Celsius.

FIG. 4 shows another embodiment of a cooling system 300 for a vacuum tube 302, according to an embodiment of the disclosure. Cooling system 300 has several components that are similar to cooling systems 10, 100, 300 of FIGS. 1, 2 and 3. For example, cooling system 300 has a vapor line 314, a liquid line 316, a condensing heat exchanger 324, an expansion reservoir 326, a pressure controller 328, a liquid bypass and equalization line 340, a solenoid valve 344, a make-up reservoir 346, an evaporating heat exchanger 318, and a pump 320. Cooling system 300 differs, however, in that it includes a sump reservoir 348 with an associated sump line 350, and spray jets 352.

Pump 320 operates in a generally similar manner to pumps 20 and 120 of FIGS. 1 and 2, respectively. Sump line 350 transfers liquid water in evaporator assembly 318 to the sump reservoir 348 for circulation back through the pump 320. Spray jets 352 direct a spray and/or spays of water directly onto the tube's anode to enhance the efficiency of the thermal contact between the boiling coolant and the surfaces from which heat energy is removed.

While spray cooling has been shown in this embodiment, in other embodiments, other enhancement techniques may be utilized to enhance cooling of the anode, including, but not limited to, using either forced cross flow boiling or jet impingement cooling techniques. Such techniques may be used in conjunction with surface enhancing configurations (e.g., pin fin configurations). Some of such configurations are described in United States patent application Ser. No. 11/420,184, which is hereby incorporated by reference.

Particular embodiments of evaporating heat exchanger 318 may provide an advantage in that spray or jet impingement of coolant may have a better heat transfer coefficient than pool boiling as described with regard to cooling system 200 of FIG. 3. Spray or jet impingement of coolant may also provide certain advantages in that cooling fins configured on the vacuum tube 302 may be made relatively smaller while realizing a relatively higher heat transfer coefficient than obtained with pool boiling with larger fins.

FIG. 5 is a flowchart showing one embodiment of a series of actions that may be performed to cool vacuum tubes using a fluid coolant operated at a sub-ambient temperature. In act 400, the process is initiated.

In act 402, evaporator assembly 18, 118, 218, or 318 receives fluid coolant in liquid form from condensing heat exchanger 24, 124, 224, or 324. The fluid coolant may be transported through evaporator assembly 18, 118, 218, or 318 and condensing heat exchanger 24, 124, 224, or 324 using any suitable approach. In one embodiment, fluid coolant is pumped using a pump 20, 120, or 320. In other embodiments, fluid coolant may be moved through evaporator assembly 18, 118, 218, or 318 and condensing heat exchanger 24, 124, 224, or 324 using convection flow of fluid coolant.

In act 404, the pressure of fluid coolant in evaporator assembly 18, 118, 218, or 318 is maintained at a sub-ambient pressure level. In a particular embodiment, the fluid coolant includes water. To control the operating pressure of the water, pressure controller 28, 128, 228, or 328 operates in conjunction with expansion reservoir 26, 126, 226, or 326 to alternatively expand or contract the volume within cooling system to maintain the pressure of the water at a sub-ambient level. A pump 20, 120, or 320 configured upstream of evaporator assembly 18, 118, 218, or 318 may cause the pressure at inlet conduits 32 to exceed a desired sub-ambient level. The pressure of water provided by pump 20, 120, or 320 may be reduced by inlet orifices 22 that restrict the flow of the water and thereby reducing its pressure. In other embodiments as described with reference to FIG. 3, control of the pressure of the water may be controlled by control box 220.

In act 406, the fluid coolant is evaporated in evaporator assembly 18, 118, 218, or 318 to vacuum tube 202 or 302. Evaporator assembly is thermally coupled to vacuum tube 202 or 302 using any suitable approach. In one embodiment, evaporator assembly 18, 118, 218, or 318 using a pool boiling mechanism that causes fluid coolant to flow in relatively close proximity to the anode of vacuum tube 202 or 302. In another embodiment, evaporator assembly 18, 118, 218, or 318 uses a spray/jet impingement cooling technique that sprays fluid coolant onto a surface that is thermally coupled to the anode of vacuum tube 202 or 302. In other embodiments, evaporator assembly 18, 118, 218, or 318 may include other surface enhancing configurations, such as a pin fin configuration.

In act 408, the evaporated fluid coolant is moved to condensing heat exchanger 24, 124, 224, or 324 where it is condensed back to it liquid phase. Once condensed, the fluid coolant may again be pumped to evaporator assembly 18, 118, 218, or 318 for further cooling of vacuum tube 202 or 302.

In act 410, air is optionally removed from the cooling system 10, 100, 200, or 300. In certain cases, unwanted air from the environment may leak into cooling system 10, 100, 200, or 300 due to sub-ambient pressures maintained inside. Air introduced into cooling system 10, 100, 200, or 300 may not evaporate in a manner similar to fluid coolant and thus may reduce the efficiency of cooling system 10, 100, 200, or 300 in certain embodiments. Air may be removed from cooling system 10, 100, 200, or 300 by pumping uncondensed mixture of vapor coolant and air to a reclamation heat exchanger 194 that condenses the vapor coolant for separation of the air. Once separated, the air may be released from the system through a vent 195.

The fluid coolant may be re-circulated through cooling system 10, 100, 200, or 300 for continued cooling of vacuum tube 202 or 302. When cooling of vacuum tube 202 or 302 is no longer needed or desired, the process ends in act 412.

Modifications, additions, or omissions may be made to the previously described method without departing from the scope of the disclosure. The method may include more, fewer, or other acts. For example, a portion of fluid coolant exiting evaporator assembly 18, 118, 218, or 318 as liquid may bypass condensing heat exchanger 24, 124, 224, or 324 by flowing through a bypass and equalization line 40, 240, or 340. Thus, cooling system 10, 100, 200, or 300 may be configured to handle process variations, such as variations in thermal loading of vacuum tube 202 or 302 that may cause a corresponding variations in the evaporation rate of its fluid coolant.

Although the present disclosure has been described with several embodiments, a myriad of changes, variations, alterations, transformations, and modifications may be suggested to one skilled in the art, and it is intended that the present disclosure encompass such changes, variations, alterations, transformation, and modifications as they fall within the scope of the appended claims. 

1. A two-phase cooling system for a vacuum tube comprising: a condensing heat exchanger that is operable to condense water from a vapor phase to a liquid phase by removing thermal energy from the water; an evaporator assembly having an inlet and an outlet that are fluidly coupled to the condensing heat exchanger, the evaporator assembly in thermal communication with a vacuum tube and operable to: receive, through the inlet, the water in the liquid phase from the condensing heat exchanger; cool the vacuum tube by transferring thermal energy from the vacuum tube to the water, the transfer of thermal energy causing the water in the liquid phase to boil and vaporize; and transport, using a pump, the vaporized water to the condensing heat exchanger through the outlet; and a pressure controller operable to maintain the pressure of the water in the evaporator assembly and the condensing heat exchanger at a sub-ambient pressure of less than three pounds-per-square-inch-absolute.
 2. A two-phase cooling system for a vacuum tube comprising: a condensing heat exchanger that is operable to condense a coolant from a vapor phase to a liquid phase by removing thermal energy from the coolant; an evaporator assembly having an inlet and an outlet that are fluidly coupled to the condensing heat exchanger, the evaporator assembly in thermal communication with a vacuum tube and operable to: receive, through the inlet, the coolant in the liquid phase from the condensing heat exchanger; cool the vacuum tube by transferring thermal energy from the vacuum tube to the coolant, the transfer of thermal energy causing the coolant in the liquid phase to boil and vaporize; and moving the vaporized coolant to the condensing heat exchanger through the outlet; and a pressure controller operable to maintain the pressure of the coolant in the evaporator assembly at a sub-ambient pressure.
 3. The two-phase cooling system of claim 2, wherein the evaporator assembly is operable to cool the vacuum tube using a pool boiling technique.
 4. The two-phase cooling system of claim 2, wherein the evaporator assembly is operable to cool the vacuum tube using a spray/jet impingement cooling technique.
 5. The two-phase cooling system of claim 2, wherein the coolant comprises water.
 6. The two-phase cooling system of claim 2, wherein the coolant comprises water and one or more antifreeze agents.
 7. The two-phase cooling system of claim 2, wherein the coolant comprises a perfluorocarbon.
 8. The two-phase cooling system of claim 2, further comprising a pump fluidly coupled between the condensing heat exchanger and the evaporator assembly, the pump operable to transport the coolant from the condensing heat exchanger to the inlet of the evaporator assembly.
 9. The two-phase cooling system of claim 2, further comprising an air removal system coupled to the condensing heat exchanger, the air removal system operable to remove air from the condensing heat exchanger and the evaporator assembly.
 10. The two-phase cooling system of claim 2, wherein the coolant comprises water and the sub-ambient pressure is less than three pounds-per-square-inch-absolute.
 11. The two-phase cooling system of claim 2, wherein the pressure controller is operable to maintain the pressure of the coolant in the condensing heat exchanger at the sub-ambient pressure.
 12. A method for cooling a vacuum tube comprising: receiving a coolant in a liquid phase from a condensing heat exchanger, the condensing heat exchanger operable to condense the coolant from a vapor phase to the liquid phase by removing thermal energy from the coolant; cooling the vacuum tube by transferring thermal energy from the vacuum tube to the coolant, the transfer of thermal energy causing the coolant in the liquid phase to boil and vaporize; moving the vaporized coolant to the condensing heat exchanger; and maintaining the coolant at a sub-ambient pressure.
 13. The method of claim 12, wherein receiving the coolant in the liquid phase comprises receiving water in the liquid phase.
 14. The method of claim 12, wherein receiving the coolant in the liquid phase comprises receiving water and one or more antifreeze agents in the liquid phase.
 15. The method of claim 12, receiving the coolant in the liquid phase comprises receiving perfluorocarbon in the liquid phase.
 16. The method of claim 12, wherein receiving the coolant from the condensing heat exchanger comprises pumping the coolant from the condensing heat exchanger using a pump.
 17. The method of claim 12, further comprising removing air from the condensing heat exchanger and the evaporator assembly using an air removal system.
 18. The method of claim 12, wherein cooling the vacuum tube by boiling and vaporizing the coolant from the liquid phase to the vapor phase comprises cooling the vacuum tube by boiling and vaporizing the coolant from the liquid phase to the vapor phase using a pool boiling technique.
 19. The method of claim 12, wherein cooling the vacuum tube by boiling and vaporizing the coolant from the liquid phase to the vapor phase comprises cooling the vacuum tube by boiling and vaporizing the coolant from the liquid phase to the vapor phase using a spray/jet impingement cooling technique.
 20. The method of claim 12, wherein maintaining the coolant at the sub-ambient pressure comprises maintaining the coolant at less than three pounds-per-square-inch-absolute.
 21. The method of claim 12, further comprising maintaining the pressure of the coolant in the condensing heat exchanger at the sub-ambient pressure. 